During well construction procedures, it is desirable to provide a filter to prevent particulate matter from the producing formation from entering the well with the produced fluids. To filter out this particulate matter, well screens are utilized which are commonly comprised of some form of slotted pipe. The size of the particulate matter excluded from flow therethrough depends upon the size of the slots. In addition to the size of the slots determining the size of the particulate matter allowed to flow therethrough, the number of slots determines the flow rate therethrough.
Fabrication of well screen commonly utilizes pipe formed from such easily formed flexible manmade materials as polyvinyl chloride, teflon and polyethelene. In order to form the slots therein, a rotary saw blade is utilized. The pipe is placed on a conveyor platform and passed under the saw blade. However, there are a number of disadvantages with utilizing a rotary saw blade with such flexible pipe. One of these disadvantages is that contact of the side of the blade with the pipe may cause binding and heating action which can cause the pipe to melt at the sawing point and result in the formation of excessively oversized and irregularly shaped slots. In addition, the cuttings resulting from passing the rotary saw blade through the pipe to form the slot have a tendency to collect on the blade surface and in the teeth of the blade. The increased friction and "binding" resulting from this packing of the slot with cuttings can cause the blade to wear out quickly.
In order to reduce the binding, a number of techniques have been utilized for cutting such materials as pipe. For example, U.S. Pat. No. 3,232,159 issued to J. H. Stanley and U.S. Pat. No. 3,066,564 issued to R. H. Carpenter both disclose the use of a mechanism for bending hose slightly such that a longitudinal strain is placed on the material to prevent binding of a single saw blade. U.S. Pat. No. 3,978,747 issued to Lyon, discloses a similar method whereby tension is continuously maintained on the surface of a tubular article being cut by progressively bending the tubular article as it is passed through a cutting blade until the device is fully severed. All of the above devices utilize relatively complicated mechanisms for bending the pipe and provide for severing of the pipe rather than slotting the pipe. Slotting, as opposed to severing of pipe, requires some form of control over both the dimension between adjacent slots and also the dimension of the slot width itself.
In view of the above disadvantages, there exists a need for a tube slotting apparatus that forms slots in a flexible tube and provides for both low cost and high efficiency operation.